Network Address Translation Overview

When a client attempts to access a server in a data center, the client incorporates its IP address in the IP header when it connects to the server. An ACE placed between the client and the server can either preserve the client IP address or translate that IP address to a routable address in the server network, based on a pool of reserved dynamic NAT addresses or a static NAT address mapping, and pass the request on to the server.

This IP address translation process is called Network Address Translation (NAT) or source NAT (SNAT). The ACE tracks all SNAT mappings to ensure that response packets from the server are routed back to the client. If your application requires that the client IP address be preserved for statistical or accounting purposes, do not implement SNAT.

Destination NAT (DNAT) translates the IP address and port of an inside host so that it appears with a publicly addressable destination IP address to the rest of the world. Typically, you configure DNAT using static NAT and port redirection. You can use port redirection to configure servers that host a service on a custom port (for example, servers hosting HTTP on port 8080).

To provide security for a server, you can map the server private IP address to a global routable IP address that a client can use to connect to the server. In this case, the ACE translates the global IP address to the server private IP address when sending data from the client to the server. Conversely, when a server responds to a client, the ACE translates the local server IP address to a global IP address for security reasons. This process is called DNAT.

You can also configure the ACE to translate TCP and UDP port numbers greater than 1024, and ICMP identifiers. This process is known as Port Address Translation (PAT). The ACE provides 64 K minus 1 K ports for each IP address for PAT. Ports 0 through 1024 are reserved and cannot be used for PAT.

By default, the ACE performs implicit PAT on flows except when:

•Only routing packets

•Only bridging packets

•Performing transparent load balancing

•Server load balancing is configured with the forward action in a policy

Some of the benefits of NAT are as follows:

•You can use private addresses on your inside networks. Private addresses are not routable on the Internet.

•NAT hides the local addresses from other networks, so attackers cannot learn the real address of a server in the data center.

•You can resolve IP routing problems, such as overlapping addresses, when you have two interfaces connected to overlapping subnets.

Dynamic NAT

Dynamic NAT, which is typically used for SNAT, translates a group of local source addresses to a pool of global source addresses that are routable on the destination network. The global pool can include fewer addresses than the local group. When a local host accesses the destination network, the ACE assigns an IP address from the global pool to the host.

Because the translation times out after being idle for a user-configurable period of time, a given user does not keep the same IP address. For this reason, users on the destination network cannot reliably initiate a connection to a host that uses dynamic NAT (even if the connection is allowed by an access control list [ACL]). Not only can you not predict the global IP address of the host, but the ACE does not create a translation unless the local host is the initiator. See the "Configuring Static NAT and Static Port Redirection" section for details about reliable access to hosts.

Note For the duration of the translation, a global host can initiate a connection to the local host if an ACL allows it. Because the address is unpredictable, a connection to the host is unlikely. However, in this case, you can rely on the security of the ACL.

Dynamic NAT has these disadvantages:

•If the global address pool has fewer addresses than the local group, you could run out of addresses if the amount of traffic is greater than expected.

Use dynamic PAT if this event occurs often, because dynamic PAT provides over 64,000 translations using multiple ports of a single IP address.

•If you need to use a large number of routable addresses in the global pool and the destination network requires registered addresses (for example, the Internet), you may encounter a shortage of usable addresses.

Note The ACE allows you to configure a virtual IP (VIP) address in the NAT pool for dynamic NAT and PAT. This action is useful when you want to source NAT real server originated connections (bound to the client) using the VIP address. This feature is specifically useful when there are a limited number of real world IP addresses on the client-side network. To perform PAT for different real servers that are source-NATed to the same IP address (VIP), you must configure the pat keyword in the nat-pool command.

The advantage of dynamic NAT is that some protocols cannot use dynamic PAT. Dynamic PAT does not work with some applications that have a data stream on one port and the control path on another, such as some multimedia applications.

Dynamic PAT

Dynamic PAT, which is also used for Stateful Network Address Translation (SNAT), translates multiple local source addresses and ports to a single global IP address and port that are routable on the destination network from a pool of IP addresses and ports reserved for this purpose. The ACE translates the local address and local port for multiple connections and/or hosts to a single global address and a unique port starting with port numbers greater than 1024.

When a local host connects to the destination network on a given source port, the ACE assigns a global IP address to it and a unique port number. Each host receives the same IP address but, because the source port number is unique, the ACE sends the return traffic, which includes the IP address and port number as the destination, to the correct host.

The ACE supports over 64,000 ports for each unique local IP address. Because the translation is specific to the local address and local port, each connection, which generates a new source port, requires a separate translation. For example, 10.1.1.1:1025 requires a separate translation from 10.1.1.1:1026.

The translation is valid only for the duration of the connection, so a user does not keep the same global IP address and port number. For this reason, users on the destination network cannot reliably initiate a connection to a host that uses dynamic PAT (even if the connection is allowed by an ACL). Not only can you not predict the local or global port number of the host, but the ACE does not create a translation unless the local host is the initiator. See the "Configuring Static NAT and Static Port Redirection" section for details about reliable access to hosts.

Dynamic PAT allows you to use a single global address, which helps to conserve routable addresses. Dynamic PAT does not work with some multimedia applications that have a data stream on a port that is different from the control path port.

Server Farm-Based Dynamic NAT

In addition to the interface-level dynamic NAT, the ACE supports dynamic NAT at the server farm level. Server farm-based dynamic NAT, which is also used for SNAT, is useful in situations where you want to perform NAT on only the IP addresses of the real servers in the primary and/or the backup server farm. Like interface-based dynamic NAT, server farm-based dynamic NAT uses a pool of IP addresses to translate a source address. Unlike interface-based NAT, server farm-based NAT translates the primary server farm IP addresses, the backup server farm IP addresses, or both.

Use this feature in the following cases:

•The ACE is configured in one-arm mode, that is, there is only one VLAN between the ACE and the Cisco Systems 6500 and 7600 Series Catalyst MSFC that is used for both client and server traffic. Both the primary and backup server farms are in the internal customer network (reachable from the same VLAN or from different VLANs), the primary server farm is Layer 2-attached, and the backup server farm is several Layer 3 hops away. In this case, perform NAT only for the backup server farm and never for the primary server farm.

•The ACE is configured in one-arm mode, the primary server farm is local, and the backup server farm is remote and reachable from the public, external network. In this case, use a private pool of IP addresses for SNAT of the primary server farm and a public, externally routable set of IP addresses for the backup server farm.

•You want to perform source NAT based on a Layer 7 rule or the selected server farm.

Static NAT

Static NAT, which is typically used for Destination NAT (DNAT), translates each local address to a fixed global address. With dynamic NAT and PAT, each host uses a different address or port after the translation times out. Because the global address is the same for each consecutive connection with static NAT, and a persistent translation rule exists, static NAT allows hosts on the global network to initiate traffic to a local host (if there is an ACL that allows it).

The main differences between dynamic NAT and static NAT are as follows:

•Static NAT uses a one-to-one correspondence between a local IP address and a fixed global IP address, while dynamic NAT assigns a global IP address from a pool of global addresses.

•With static NAT, you need an equal number of global IP addresses and local IP addresses. With dynamic NAT, you can have a pool of fewer global addresses than local addresses.

Static Port Redirection

Static port redirection, also used for DNAT, performs the same function as static NAT and additionally translates TCP or UDP ports or ICMP identifiers for the local and global addresses. With static port redirection, you can use the same global address in multiple static NAT statements, provided that, along with the address, you use different port numbers.

For example, if you want to provide a single address for global users to access FTP, HTTP, and SMTP, but there are different servers for each protocol on the local network, you can specify static port redirection statements for each server that use the same global IP address with different ports.

Maximum Number of NAT Commands

The ACE supports the following maximum numbers of nat, nat-pool, and natstatic commands divided among all contexts:

•nat command—8192

•nat-pool command—8192

•nat static command—8192

Global Address Guidelines

When you translate the local address to a global address, you can use the following global addresses:

•Addresses on the same network as the global interface—If you use addresses on the same network as the global interface (through which traffic exits the ACE), the ACE uses proxy ARP to answer any requests for translated addresses and thus intercepts traffic destined for a local address. This solution simplifies routing, because the ACE does not need to be the gateway for any additional networks. However, this approach does put a limit on the number of available addresses used for translations.

Note You cannot use the IP address of the global interface for NAT or PAT.

•Addresses on a unique network—If you need more addresses than are available on the global interface network, you can identify addresses on a different subnet. The ACE uses proxy ARP to answer any requests for translated addresses, so it intercepts traffic destined for a local address. You need to add a static route on the upstream router that sends traffic destined for the translated addresses on the ACE.

You cannot configure global IP address ranges across subnets. For example, the following command is not allowed and will generate an Invalid IP address error: nat-pool 2 10.0.6.1 10.0.7.20 netmask 255.255.255.0.

You must configure a netmask when configuring a NAT pool. A netmask of 255.255.255.255 instructs the ACE to use all the IP addresses in the range.

Configuring an Idle Timeout for NAT

You can configure an idle timeout for NAT by using the timeout xlate command in configuration mode. The syntax of this command is as follows:

timeout xlate seconds

The seconds argument is an integer from 60 to 2147483. The default is 10800 seconds (3 hours). The seconds value determines how long the ACE waits to free the Xlate slot after it becomes idle.

For example, to specify an idle timeout of 120 seconds (2 minutes), enter:

host1/Admin(config)# timeout xlate 120

To reset the NAT idle timeout to the default value of 10800 seconds, enter:

host1/Admin(config)# no timeout xlate 120

Configuring Dynamic NAT and PAT

This section describes how to configure dynamic NAT and PAT on an ACE for SNAT. For overview information about dynamic NAT and dynamic PAT, see the "Network Address Translation Overview" section. This section contains the following topics:

Dynamic NAT and PAT Configuration Quick Start

Table 5-1 provides a quick overview of the steps required to configure dynamic NAT and PAT. Each step includes the CLI command or a reference to the procedure required to complete the task. For a complete description of each feature and all the options associated with the CLI commands, see the sections following Table 5-1.

Table 5-1 Dynamic NAT and PAT Configuration Quick Start

Task and Command Example

1. If you are operating in multiple contexts, observe the CLI prompt to verify that you are operating in the desired context. If necessary, change to the correct context.

host1/Admin# changeto C1

host1/C1#

The rest of the examples in this table use the C1 user context, unless otherwise specified. For details on creating contexts, see the Cisco 4700 Series Application Control Engine Appliance Virtualization Configuration Guide.

Configuring Interfaces for Dynamic NAT and PAT

Configure an interface for clients and an interface for the real servers. If you are operating the ACE in one-arm mode, do not configure an interface for clients. For details, see the Cisco 4700 Series Application Control Engine Appliance Routing and Bridging Configuration Guide.

Creating a Global IP Address Pool for NAT

Dynamic NAT uses a pool of global IP addresses that you specify. You can define either a single global IP address for a group of servers with PAT to differentiate between them, or a range of global IP addresses when using dynamic NAT only. To use a single IP address or a range of addresses, you assign an identifier to the address pool. You configure the NAT pool on the server VLAN interface.

Note If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated.

To create a pool of IP addresses for dynamic NAT, use the nat-pool command in interface configuration mode. The syntax of this command is as follows:

nat-poolpool_idip_address1[ip_address2]netmaskmask[pat]

The keywords, arguments, and options are as follows:

•pool_id—Identifier of the NAT pool of global IP addresses. Enter an integer from 1 to 2147483647.

Note If you configure more than one NAT pool with the same ID, the ACE uses the last-configured NAT pool first, and then the other NAT pools.

•ip_address1—Single IP address, or if also using the ip_address2 argument, the first IP address in a range of global addresses used for NAT. Enter an IP address in dotted-decimal notation (for example, 172.27.16.10).

•ip_address2—(Optional) Highest IP address in a range of global IP addresses used for NAT. Enter an IP address in dotted-decimal notation (for example, 172.27.16.109). You can configure a maximum of 64 K addresses in a NAT pool.

If you specify PAT, you can configure a maximum of 32 IP addresses in a NAT pool range. You cannot configure an IP address range across subnets. For example, the following command is not allowed and will generate an Invalid IP address error: nat-pool 2 10.0.6.1 10.0.7.20 netmask 255.255.255.0.

Note The ACE allows you to configure a virtual IP (VIP) address in the NAT pool for dynamic NAT and PAT. This action is useful when you want to source NAT real server originated connections (bound to the client) using the VIP address. This feature is specifically useful when there are a limited number of real world IP addresses on the client-side network. To perform PAT for different real servers that are source-NATed to the same IP address (VIP), you must configure the pat keyword in the nat-pool command.

•netmaskmask—Specifies the subnet mask for the IP address pool. Enter a mask in dotted-decimal notation (for example, 255.255.255.255). A network mask of 255.255.255.255 instructs the ACE to use all the IP addresses in the specified range.

Note Before you can remove a NAT pool from an interface, you must remove the service policy and the policy map associated with the NAT pool.

To remove a NAT pool from the configuration, enter:

host1/C1(config-if)# no nat-pool 1

Configuring a Class Map

You can configure a traffic class for dynamic NAT and PAT by using the class-map command in configuration mode. For more information about class maps, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

The syntax of this command is as follows:

class-map match-any name

The name argument is a unique identifier for the class map, specified as an unquoted text string with a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# class-map match-any NAT_CLASS

host1/C1(config-cmap)#

To remove a class-map from the configuration, enter:

host1/C1(config)# no class-map match-any NAT_CLASS

Enter match criteria for the ACL or the client source address using the match command in class-map configuration mode. For example, enter:

Configuring a Class Map for Passive FTP

If you are using passive FTP with source NAT, you must configure an additional class map to source NAT the passive data connection. You then associate this class map with the Layer 4 multimatch policy and configure the nat dynamic command as an action in the policy map under this class map. To configure a class map for passive FTP, enter the following commands:

host1/C1(config)# class-map match-any FTP_NAT_CLASS

host1/C1(config-cmap)# match virtual address 172.16.35.37 any

Configuring a Policy Map

You can configure a traffic policy for dynamic NAT and PAT by using the policy-map command in configuration mode. For more information about policy maps, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

The syntax of this command is as follows:

policy-map multi-match name

The name argument is the name assigned to the policy map. Enter an unquoted text string with no spaces and a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# policy-map multi-match NAT_POLICY

host1/C1(config-pmap)#

To remove a policy map from the configuration, enter:

host1/C1(config)# no policy-map multi-match NAT_POLICY

Associate the previously created class map with the policy map. For example, enter:

host1/C1(config-pmap)# class NAT_CLASS

host1/C1(config-pmap-c)#

To dissociate a class map from a policy map, enter:

host1/C1(config-pmap)# no class NAT_CLASS

Configure policy-map actions as required. For example, configure:

host1/C1(config-pmap-c)# loadbalance policy L7_POLICY

host1/C1(config-pmap-c)# loadbalance VIP inservice

For passive FTP, associate the FTP_NAT_CLASS class map (see the Configuring a Class Map for Passive FTP section) with the Layer 4 policy map. For example, enter the following commands in policy map configuration mode:

host1/C1(config)# policy-map multi-match NAT_POLICY

host1/C1(config-pmap)# class FTP_NAT_CLASS

Proceed with the following section and configure the nat dynamic command as a policy action under the FTP class map if you are using passive FTP. Otherwise, configure the nat dynamic command as a policy action under the NAT_CLASS class map.

You can configure dynamic NAT and PAT (SNAT) as an action in a Layer 3 and Layer 4 policy map by using the nat dynamic command in policy-map class configuration mode. The ACE applies dynamic NAT from the interface to which the traffic policy is attached (through the service-policy interface configuration command) to the interface specified in the nat command. If you are operating in one-arm mode, there is only one VLAN interface.

The syntax of this command is as follows:

natdynamicpool_id vlan number

The keywords, arguments, and options are as follows:

•dynamic pool_id—Refers to the identifier of a global pool of IP addresses that was configured using the nat-pool command on the specified VLAN (see the "Creating a Global IP Address Pool for NAT" section). Dynamic NAT translates a group of local source IP addresses to a pool of global IP addresses that are routable on the destination network. All packets egressing the interface attached to the traffic policy have their source address translated to one of the available addresses in the global pool. Enter an integer from 1 to 2147483647.

•vlan number—Specifies the server interface for the global IP address. This interface must be different from the interface that the ACE uses to filter and receive traffic that requires NAT, unless the network design operates in one-arm mode. In that case, the VLAN number is the same.

Note If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated.

The following example specifies the nat command as an action for a dynamic NAT Layer 3 and Layer 4 policy map:

host1/C1(config)# policy-map multi-action NAT_POLICY

host1/C1(config-pmap)# class NAT_CLASS

host1/C1(config-pmap-c)# nat dynamic 1 vlan 200

To remove a dynamic NAT action from a policy map, enter:

host1/C1(config-pmap-c)# no nat dynamic 1 vlan 200

Applying the Dynamic NAT and PAT Policy Map to an Interface Using a Service Policy

Activate the dynamic NAT and PAT policy map and associate it with an interface by using the service-policy command in interface configuration mode. For details about the service-policy command, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

Note You can configure dynamic NAT as an input service policy only, not as an output service policy. You cannot apply the same NAT policy both locally and globally.

The syntax of this command is as follows:

service-policyinputpolicy_name

The keywords and arguments are as follows:

•input—Specifies that the traffic policy is to be attached to the input direction of a VLAN interface. The traffic policy evaluates all traffic received by that interface.

•policy_name—Name of a previously defined policy map. The name can have a maximum of 64 alphanumeric characters.

For example, to apply a service policy to a specific interface, enter:

host1/C1(config)# interface vlan 100

host1/C1(config-if)# mtu 1700

host1/C1(config-if)# ip address 192.168.1.100 255.255.255.0

host1/C1(config-if)# service-policy input NAT_POLICY

To apply a service policy globally to all interfaces in a context, enter:

host1/C1(config)# service-policy input NAT_POLICY

To remove a service policy from an interface, enter:

host1/C1(config-if)# no service-policy input NAT_POLICY

To remove a service policy globally from all interfaces in a context, enter:

host1/C1(config)# no service-policy input NAT_POLICY

Note When you detach a traffic policy either individually from the last VLAN interface on which you applied the service policy or globally from all VLAN interfaces in the same context, the ACE automatically resets the associated service-policy statistics. The ACE performs this action to provide a new starting point for the service-policy statistics the next time that you attach a traffic policy to a specific VLAN interface or globally to all VLAN interfaces in the same context.

Configuring Server Farm-Based Dynamic NAT

This section describes how to configure server farm-based dynamic NAT on an ACE for SNAT. For overview information about server farm-based dynamic NAT, see the "Network Address Translation Overview" section. This section contains the following topics:

Server Farm-Based Dynamic NAT Configuration Quick Start

Table 5-2 provides a quick overview of the steps required to configure server farm-based dynamic NAT. Each step includes the CLI command or a reference to the procedure required to complete the task. For a complete description of each feature and all the options associated with the CLI commands, see the sections following Table 5-2.

Table 5-2 Sever Farm-Based Dynamic NAT Configuration Quick Start

Task and Command Example

1. If you are operating in multiple contexts, observe the CLI prompt to verify that you are operating in the desired context. If necessary, change to the correct context.

host1/Admin# changeto C1

host1/C1#

The rest of the examples in this table use the C1 user context, unless otherwise specified. For details on creating contexts, see the Cisco 4700 Series Application Control Engine Appliance Virtualization Configuration Guide.

9. Configure server farm-based dynamic NAT as a policy-map action in the Layer 7 load-balancing policy. You can configure multiple instances of this command for each primary and backup serverfarm and each outgoing server VLAN.

Configuring Interfaces for Server Farm-Based Dynamic NAT

Configure an interface for clients and an interface for the real servers. If you are operating the ACE in one-arm mode, omit the client interface. For details about configuring interfaces, see the Cisco 4700 Series Application Control Engine Appliance Routing and Bridging Configuration Guide.

Creating a Global IP Address Pool for Dynamic NAT

Dynamic NAT uses a pool of global IP addresses that you specify. You can define a range of global IP addresses when using dynamic NAT. To use a range of addresses, you assign an identifier to the address pool. You then associate the NAT pool with the server VLAN interface.

Note If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated.

To create a pool of IP addresses for dynamic NAT, use the nat-pool command in interface configuration mode. The syntax of this command is as follows:

nat-poolpool_idip_address1ip_address2netmaskmask

The keywords, arguments, and options are as follows:

•pool_id—Identifier of the NAT pool of global IP addresses. Enter an integer from 1 to 2147483647.

Note If you configure more than one NAT pool with the same ID, the ACE uses the last-configured NAT pool first, and then the other NAT pools.

•ip_address1—Single IP address, or if also using the ip_address2 argument, the first IP address in a range of global addresses used for NAT. Enter an IP address in dotted-decimal notation (for example, 172.27.16.10).

•ip_address2—Highest IP address in a range of global IP addresses used for NAT. Enter an IP address in dotted-decimal notation (for example, 172.27.16.26). You can configure a maximum of 64 K addresses in a NAT pool.

You cannot configure an IP address range across subnets. For example, the following command is not allowed and will generate an Invalid IP address error: nat-pool 2 10.0.6.1 10.0.7.20 netmask 255.255.255.0.

Note The ACE allows you to configure a virtual IP (VIP) address in the NAT pool for dynamic NAT. This action is useful when you want to source NAT real server originated connections (bound to the client) using the VIP address. This feature is specifically useful when there are a limited number of real world IP addresses on the client-side network.

•netmaskmask—Specifies the subnet mask for the IP address pool. Enter a mask in dotted-decimal notation (for example, 255.255.255.255). A network mask of 255.255.255.255 instructs the ACE to use all the IP addresses in the specified range.

To configure a NAT pool consisting of a range of 32 global IP addresses, enter:

To associate the previously created class map with the policy map. For example, enter:

host1/C1(config-pmap-lb)# class L7_CLASS

host1/C1(config-pmap-lb-c)#

To disassociate a class map from a policy map, enter:

host1/C1(config-pmap-lb)# no class L7_CLASS

Configuring Server Farm-Based Dynamic NAT as a Layer 7 Policy Action

Configure server farm-based dynamic NAT as an action in a Layer 7 load-balancing policy map by using the nat command in policy-map load-balancing class configuration mode. Typically, you use dynamic NAT for SNAT. Dynamic NAT allows you to identify local traffic for address translation by specifying the source and destination addresses in an extended ACL, which is referenced as part of the class map traffic classification. The ACE applies dynamic NAT from the interface to which the traffic policy is attached (through the service-policy interface configuration command) to the interface specified in the nat dynamic command.

The syntax of this command is as follows:

nat dynamic pool_id vlannumber serverfarm {primary | backup}

The keywords and arguments are as follows:

•pool_id—Identifier of the NAT pool of global IP addresses. Enter an integer from 1 to 2147483647.

Note If you configure more than one NAT pool with the same ID, the ACE uses the last-configured NAT pool first, and then the other NAT pools.

•vlan number—Specifies the server interface for the global IP address. This interface must be different from the interface that the ACE uses to filter and receive traffic that requires NAT, unless the network design operates in one-arm mode. In that case, the VLAN number is the same.

•serverfarm—Specifies server farm-based dynamic NAT.

•primary | backup—Specifies that the dynamic NAT applies to either the primary server farm or the backup server farm.

Note If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated.

The following SNAT server farm-based dynamic NAT example specifies the nat command as an action for a Layer 7 policy map:

Configure a Layer 3 and Layer 4 traffic class for server farm-based dynamic NAT by using the class-map command in configuration mode. For more information about class maps, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

The syntax of this command is as follows:

class-map match-any name

The name argument is a unique identifier for the class map, specified as an unquoted text string with a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# class-map match-any NAT_CLASS

host1/C1(config-cmap)#

To remove a class map from the configuration, enter:

host1/C1(config)# no class-map match-any NAT_CLASS

Enter match criteria as required using the match command in class-map configuration mode. For example, enter:

Configure a Layer 3 and Layer 4 traffic policy for NAT by using the policy-map command in configuration mode. For more information about policy maps, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

The syntax of this command is as follows:

policy-map multi-match name

The name argument is the name assigned to the policy map. Enter an unquoted text string with no spaces and a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# policy-map multi-match NAT_POLICY

host1/C1(config-pmap)#

To remove a policy map from the configuration, enter:

host1/C1(config)# no policy-map multi-match NAT_POLICY

To associate the previously created class map with the policy map. For example, enter:

host1/C1(config-pmap)# class NAT_CLASS

host1/C1(config-pmap-c)#

To dissociate a class map from a policy map, enter:

host1/C1(config-pmap)# no class NAT_CLASS

Configure policy-map actions as required. For example, configure:

host1/C1(config-pmap-c)# loadbalance policy L7_POLICY

host1/C1(config-pmap-c)# loadbalance VIP inservice

Applying the Layer 3 and Layer 4 Policy Map to an Interface Using a Service Policy

You can activate the server farm-based dynamic NAT policy and assign it to an interface by using the service-policy command in interface configuration mode. For details about the service-policy command, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

Note You can configure dynamic NAT as an input service policy only, not as an output service policy. You cannot apply the same NAT policy both locally and globally.

The syntax of this command is as follows:

service-policyinputpolicy_name

The keywords and arguments are as follows:

•input—Specifies that the traffic policy is to be attached to the input direction of a VLAN interface. The traffic policy evaluates all traffic received by that interface.

•policy_name—Name of a previously defined policy map. The name can have a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# interface vlan 100

host1/C1(config-if)# mtu 1700

host1/C1(config-if)# ip address 192.168.12.100 255.255.255.0

host1/C1(config-if)# service-policy input NAT_POLICY

To remove a service policy from an interface, enter:

host1/C1(config-if)# no service-policy input NAT_POLICY

Note When you remove a traffic policy from the last VLAN interface on which you applied the service policy, the ACE automatically resets the associated service-policy statistics. The ACE performs this action to provide a new starting point for the service-policy statistics the next time that you attach a traffic policy to a specific VLAN interface.

Configuring Static NAT and Static Port Redirection

This section describes how to configure static NAT and static port redirection on an ACE for DNAT. For overview information about static NAT and static port redirection, see the "Network Address Translation Overview" section. This section contains the following topics:

Static NAT Configuration Quick Start

Table 5-3 provides a quick overview of the steps required to configure static NAT and static port redirection. Each step includes the CLI command or a reference to the procedure required to complete the task. For a complete description of each feature and all the options associated with the CLI commands, see the sections following Table 5-3.

Table 5-3 Static NAT Configuration Quick Start

Task and Command Example

1. If you are operating in multiple contexts, observe the CLI prompt to verify that you are operating in the desired context. If necessary, change to the correct context.

host1/Admin# changeto C1

host1/C1#

The rest of the examples in this table use the C1 user context, unless otherwise specified. For details on creating contexts, see the Cisco 4700 Series Application Control Engine Appliance Virtualization Configuration Guide.

Configuring Interfaces for Static NAT and Static Port Redirection

Configure an interface for clients and an interface for the real servers. For details, see the Cisco 4700 Series Application Control Engine Appliance Routing and Bridging Configuration Guide.

Configuring a Class Map

You can configure a traffic class for static NAT and port redirection by using the class-map command in configuration mode. For more information about class maps, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

The syntax of this command is as follows:

class-map match-any name

The name argument is a unique identifier for the class map, specified as an unquoted text string with a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# class-map match-any NAT_CLASS

host1/C1(config-cmap)#

To remove a class-map from the configuration, enter:

host1/C1(config)# no class-map match-any NAT_CLASS

Enter match criteria as required using the match command in class-map configuration mode. For example, enter:

host1/C1(config-cmap)# match access-list NAT_ACCESS

or

host1/C1(config-cmap)# match source address 192.168.12.15

To remove a match statement from a class map, enter:

host1/C1(config-cmap)# no match access-list NAT_ACCESS

Configuring a Policy Map

You can configure a traffic policy for NAT by using the policy-map command in configuration mode. For more information about policy maps, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

The syntax of this command is as follows:

policy-map multi-match name

The name argument is the name assigned to the policy map. Enter an unquoted text string with no spaces and a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# policy-map multi-match NAT_POLICY

host1/C1(config-pmap)#

To remove a policy map from the configuration, enter:

host1/C1(config)# no policy-map multi-match NAT_POLICY

To associate the previously created class map with the policy map. For example, enter:

host1/C1(config-pmap)# class NAT_CLASS

host1/C1(config-pmap-c)#

To dissociate a class map from a policy map, enter:

host1/C1(config-pmap)# no class NAT_CLASS

Configuring Static NAT and Static Port Redirection as a Policy Action

You can configure static NAT and static port redirection as an action in a policy map by using the nat static command in policy-map class configuration mode. Typically, you use static NAT and port redirection for DNAT. Static NAT allows you to identify local traffic for address translation by specifying the source and destination addresses in an extended ACL, which is referenced as part of the class map traffic classification. The ACE applies static NAT from the interface to which the traffic policy is attached (through the service-policy interface configuration command) to the interface specified in the nat static command.

•static ip_address—Sets up a single static translation. The ip_addressargument establishes the globally unique IP address of a host as it appears to the outside world. The policy map performs the global IP address translation for the source IP address specified in the ACL (as part of the class-map traffic classification).

•port1—Global TCP or UDP port for static port redirection. Enter an integer from 0 to 65535.

•tcp eqport2—Specifies a TCP port name or number. Enter an integer from 0 to 65535. A value of 0 instructs the ACE to match any port. Alternatively, you can enter a protocol keyword that corresponds to a TCP port number. See Table 5-4 for a list of supported well-known TCP port names and numbers.

Table 5-4 Well-Known TCP Port Numbers and Keywords

Keyword

Port Number

Description

ftp

21

File Transfer Protocol

http

80

Hypertext Transfer Protocol

https

443

HTTP over TLS/SSL

irc

194

Internet Relay Chat

matip-a

350

Mapping of Airline Traffic over Internet Protocol (MATIP) Type A

nntp

119

Network News Transport Protocol

pop2

109

Post Office Protocol v2

pop3

110

Post Office Protocol v3

rtsp

554

Real Time Streaming Protocol

smtp

25

Simple Mail Transfer Protocol

telnet

23

Telnet

•udp eqport3—Specifies a UDP port name or number. Enter an integer from 0 to 65535. A value of 0 instructs the ACE to match any port. Alternatively, you can enter a protocol keyword that corresponds to a UDP port number. See Table 5-5 for a list of supported well-known UDP port names and numbers.

Table 5-5 Well-Known UDP Port Numbers and Keywords

Keyword

Port Number

Description

dns

53

Domain Name System

wsp

9200

Connectionless Wireless Session Protocol (WSP)

wsp-wtls

9202

Secure Connectionless WSP

wsp-wtp

9201

Connection-based WSP

wsp-wtp-wtls

9203

Secure Connection-based WSP

•vlan number—Specifies the interface for the global IP address.

Note If a packet egresses an interface that you have not configured for NAT, the ACE transmits the packet untranslated.

The following DNAT static port redirection example specifies the nat static command as an action for a static NAT policy map:

Applying the Static NAT and Static Port Redirection Policy Map to an Interface Using a Service Policy

You can activate the static NAT and port redirection policy and assign it to an interface by using the service-policy command in interface configuration mode. For details about the service-policy command, see the Cisco 4700 Series Application Control Engine Appliance Administration Guide.

Note You can configure static NAT as an input service policy only; you cannot configure it as an output service policy.

The syntax of this command is as follows:

service-policyinputpolicy_name

The keywords and arguments are as follows:

•input—Specifies that the traffic policy is to be attached to the input direction of a VLAN interface. The traffic policy evaluates all traffic received by that interface.

•policy_name—Name of a previously defined policy map. The name can have a maximum of 64 alphanumeric characters.

For example, enter:

host1/C1(config)# interface vlan 100

host1/C1(config-if)# mtu 1700

host1/C1(config-if)# ip address 192.168.1.100 255.255.255.0

host1/C1(config-if)# service-policy input NAT_POLICY

To remove a service policy from an interface, enter:

host1/C1(config-if)# no service-policy input NAT_POLICY

Note When you remove a traffic policy from the last VLAN interface on which you applied the service policy, the ACE automatically resets the associated service-policy statistics. The ACE performs this action to provide a new starting point for the service-policy statistics the next time that you attach a traffic policy to a specific VLAN interface.

Displaying NAT Configurations and Statistics

The following sections describe the commands used to display dynamic and static NAT and PAT configurations and statistics:

•global ip_address1 ip_address2—(Optional) Displays information for a global IP address or range of global IP addresses to which the ACE translates source addresses for static and dynamic NAT. For a single global IP address, enter the address in dotted-decimal notation (for example, 192.168.12.15). To specify a range of IP addresses, enter a second IP address.

•netmaskmask—(Optional) Displays the subnet mask for the specified IP addresses.

•localip_address3 ip_address4—(Optional) Displays the local IP address or range of local IP addresses. For a single local IP address, enter the address in dotted-decimal notation (for example, 192.168.12.15). To specify a range of local IP addresses, enter a second IP address.

•gportport1 port2—(Optional) Displays information for a global port or a range of global ports to which the ACE translates source ports for static port redirection and dynamic PAT, respectively. Enter a port number as an integer from 0 to 65535. To specify a range of port numbers, enter a second port number.

•lportport3 port4—(Optional) Displays information for a local port or a range of local ports. Enter a port number as an integer from 0 to 65535. To specify a range of port numbers, enter a second port number.

Dynamic NAT Example

The following example output of the show xlate command shows dynamic NAT (SNAT in this example). When a user uses Telnet from 172.27.16.5 in VLAN 2020, the ACE translates it to 192.168.100.1 in VLAN 2021.

host1/Admin# show xlate global 192.168.100.1 192.168.100.10

NAT from vlan2020:172.27.16.5 to vlan2021:192.168.100.1 count:1

Dynamic PAT Example

The following example shows dynamic PAT. When a user uses Telnet from 172.27.16.5 in VLAN 2020, the ACE translates it to 192.168.201.1 in VLAN 2021.

host1/Admin# show xlate

TCP PAT from vlan2020:172.27.16.5/38097 to vlan2021:192.168.201.1/1025

Static NAT Example

The following example shows static NAT. The ACE maps a real IP address (172.27.16.5) to 192.168.210.1.

Static Port Redirection (Static PAT) Example

The following example shows static port redirection (DNAT in this example). A host at 192.168.0.10:37766 uses Telnet to connect to 192.168.211.1:3030 on VLAN 2021 on the ACE. The ACE maps 172.27.0.5:23 on VLAN 2020 to 192.168.211.1:3030 on VLAN 2021.

Clearing Xlates

You can clear the global address-to-local address mapping information based on the global address, the global port, the local address, the local port, the interface address as the global address, and the NAT type by using the clear xlate command in Exec mode. When you enter this command, the ACE releases sessions that are using the translations (Xlates). The syntax of this command is as follows:

Note If you configured redundancy, then you need to explicitly clear Xlates on both the active and the standby ACEs. Clearing Xlates on the active appliance alone will leave the standby appliance's Xlates at the old mappings.

For example, to clear all static translations, enter:

host1/Admin# clear xlate state static

NAT Configuration Examples

The following sections show typical scenarios that use dynamic and static NAT solutions:

Dynamic NAT and PAT (SNAT) Configuration Example

The following SNAT configuration example shows the commands that you use to configure dynamic NAT and PAT on your ACE. In this SNAT example, packets that ingress the ACE from the 192.168.12.0 network are translated to one of the IP addresses in the NAT pool defined on VLAN 200 by the nat-pool command. The pat keyword indicates that ports higher than 1024 are also translated.

If you are operating the ACE in one-arm mode, omit interface VLAN 100 and configure the service policy on interface VLAN 200.

Server Farm-Based Dynamic NAT (SNAT) Configuration Example

The following SNAT configuration example shows the commands that you use to configure server farm-based dynamic NAT on your ACE. In this SNAT example, real servers addresses on the 172.27.16.0 network are translated to one of the IP addresses in the NAT pool defined on VLAN 200 by the nat-pool command.

If you are operating the ACE in one-arm mode, omit interface VLAN 100 and configure the service policy on interface VLAN 200.

Static Port Redirection (DNAT) Configuration Example

The following DNAT configuration example shows those sections of the running configuration related to the commands necessary to configure static port redirection on your ACE. Typically, this configuration is used for DNAT, where HTTP packets that are destined to 192.0.0.0/8 and ingressing the ACE on VLAN 101 are translated to 10.0.0.0/8 and port 8080. In this example, the servers are hosting HTTP on custom port 8080.

SNAT with Cookie Load Balancing Example

The following configuration example shows those sections of the running configuration related to the commands necessary to configure SNAT (dynamic NAT) with cookie load balancing. Any source host that sends traffic to the VIP 20.11.0.100 is translated to one of the free addresses in the NAT pool in the range 30.11.100.1 to 30.11.200.1, inclusive. If you want to use PAT instead of NAT, replace "nat dynamic 1 vlan 2021" with "nat dynamic 2 vlan 2021" in the L7SLBCookie policy map.